Electrical discharge device



1936- J. ca. w. MULDER ET AL 2,051,457

ELECTRICAL DISCHARGE DEVICE Filed NOV. 28, 1952 Patented Aug. 18, 1936ELECTRICAL DISCHARGE DEVICE Johannes Gijsbertus Wilhelm Mulder, JohannesBruijnes, and Johannes Hendrikus Josephus 'Maartens, Eindhoven,Netherlands, assignors to N. V. Philips hoven, NetherlandsGloeilampenfabriken, Eind- Application Novemben28, 1932, Serial No.644,724

In Germany D ecember 9, 1931 6 Claims. (Cl. 250-275) The presentinvention relates to electrical discharge devices and more particularbto a novel anode construction for discharge tubes.

In certain types of discharge devices, for instance in heavy dutygas-filled rectifying tubes with thermionic cathodes, the anode assumesduring operation a high temperature, which for instance, in gas-filledrectifier tubes is primarily due to its bombardment by the ions. Suchoverheating of the anode is objectionable as it adversely affects theoperating characteristics and life of the tube. To prevent suchoverheating of the anode various means have been suggested in the past,none of which however has been quite successful.

One way of reducing the anode temperature is by increasing the size ofthe anode, but this correspondingly increases the weight of the anode. Aheavier anode not only. requires heavier supports but is speciallyobjectionable in case of glass containers as it increases the load to becarried by the seal and the vitreous envelope of the tube. For instancean otherwise very advantageous seal and support construction, consistingof a chrome-iron disc sealed to one end of the vitreous container andsupporting the anode by means of an intermediate rod is unsuitable forheavy anodes as the seal is liable to crack under the weight andmomentum of the anode.

It has also been proposed to increase the cooling surface of the anodeby means of corrugations provided thereon. However, this gives rise toundesired electron emission from the anode especially at the sharp edgesof the corrugations.

It has also been suggested to lighten the anode by means of opencavities provided, for instance, on its side turned away from thecathode. Such construction, however, gives rise to a glow discharge inthe cavity, with consequent back discharge between the anode and thecathode.

The present invention provides a novel and simple construction whichpermits the anode to be provided with a large cooling area withoutproducing the disadvantages of large weight, undesired electronemission, back discharge, etc.

According to the invention the anode is provided with a large andpreferably smooth outside area and the anode is lightened by providingit with one or more interior cavities which are fully enclosed and thusare not in communication with the discharge space or with parts outsidethe tube.

The thickness of the walls of such a hollow anode may be reduced to suchextent as is safe for mechanical considerations, and thus a very light,large area anode can be obtained. As the cavity is closed, theelectrical conditions prevailing therein have no disturbing influenceson the discharge of the tube.

The invention can'bc applied to anodesconsisting of non-metallicmaterials, for instance, graphite and carbon, which are speciallyadapted for gas-filled rectifier tubes, as well as to metal anodes.

The invention will be more fully described in connection with theaccompanying drawing forming part of this specification which shows asexamples specific embodiments of my invention and in which:

Figure 1 is a longitudinal section of a rectifying tube embodying ananode construction according to our invention.

Fig. 2 is a sectional elevation of a modified anode constructionaccording to our invention.

Figure 3 is a side view, partly in section, of a three electrodedischarge tube, comprising a still further embodiment of an anodeaccording to our invention.

Referring to Figure 1 there is shown a rectifying tube comprising avitreous envelope 1 having a reentrant portion carrying a stem 2 onwhich is supported a filamentary cathode 3, the two ends of which areconnected to lead-in wires 8 and 9. The anode is supported by achrome-iron disc 4 sealed in the opposite end of the envelope I and iscarried. by a suitable metal rod it which may be integral with the disc4 or may be welded, soldered or otherwise secured thereto. The stem It]carries a cylindrical carbon or 5 which is provided with internalthreaded carbon plug 6 is tightly block 5 to engage its threads Icompletely closes the cavity ll.

It should be well understood that the cavity H can take up the majorportion of the block 5, the walls of which can be reduced to such extentthat their thickness is merely determined by the requirementofmechanical strength. It is obvious that a very large effectiveanode-area may be obtained with a comparatively low weight of the anode.7

Instead of providing a threaded joint between the block 5 and the plug6, a suitable tight fit may otherwise be obtained, for instance, bypressing the plug 6 into the block 5.

The incandescent cathode is preferably provided with a high electronemitting surface, for instance, an earth oxide layer, and an indirectlyheated cathode may be used instead of the dithreads l2. A screwed in the2 and thereby graphite block rectly heated cathode shown in the drawing.As a rule there is also provided a gas filling, for instance, mercuryvapor or a rare gas or a combination of both.

Constructions as shown in Figs. 1 and 2 have been found especiallyadvantageous in gas-filled thermionic rectifier tubes for currents ofamps. and more voltsand more. In such tubes the gas is preterably argonof pressure of some microns to several mm. The anode is preferably ofcarbon or graphite or of a refractory metal as zirconium carbonized atitssurface. An anode as shown in' these figures'm'ay have for instance aheight of 5 cm. and 'a diameter "of 3cm; in this case the 'cavity has adepth of about 2 cm. and a diameter of about :2 cm.

Figure 2 shows a modification-0f the anodeconstruction in which the plug6 is provided with a fiange 1 which when the plug is screwed in theblock 5 abuts with its upper face against the free end face-l3 of theblock. The two 00- V operatingfaces are preferably machined-to prosameor of different materials.

of proper supports a cathode 2.3,

'vide for a tight fit.

The block and the plug may be made .of the Our invention can beialsoapplied to tubes j 'hav'ing more than two electrodes. .Forzinstancein Fig. 3 there is shown a 'tubeembodying our invention in which avitreous container 2| .is .provided with a stem 22 which carries .bymeans a heater .24 .for the indirect heating-of the cathode andvdisposed within the cathode, a .grid 21 surrounding the cathode and ananode: 25 surrounding the .grid. The anode 25 is shown as formed of ahollow metal 'ring preferably of a refractory metal. The ring 25 canbeformed, for instance, (byv joining a two part casting or it may bemade of sheet metal'formed into proper shape and welded togetherzto formaclosed hollow ring member.

. While cylindrically, shaped anodes, as .shown in Figs. 1 to 3 provideas a rule for themost icompact construction my inventioncan.besapplied-to anodes having other shapes, or instead :of a singlecavity a plurality .of cavitiesmay beprovided, each being closed by :aplug or otherwise. Various other modifications may suggest themselvesand. :we do not wish to be limited tothe examples shown and described,.but desire'the appended claims to be.:construed as broadly aspermissible in .view of theprior In the claims the term carbon shallinclude also graphite and :other. carbon modifications adapted to serveas anode material.

What we:claim is:

r 1. A rectifier tube for currents of 20 amperes or more, comprising. anenvelopezzand a .gaseous filling therein, a thermionic oxide cathodeland ..a cooperating anode; a discharge :space being formed between saidanode and cathode, said anode having a cylindrical shape'zandi av largesurface area and being provided with a bore which substantially reducesthe weight of the anode, said bore being void of non-gaseous mat- :terand being ,closed'by a plug member at its .end opposing the cathode. H

and for voltages up to 100,000 7 *matter, a chrome-iron member sealed at:velope, a gaseous filling 2. A rectifier tube comprising an envelopeand a gaseous filling therein, a cathode and a cooperating anode, adischarge space being formed between said anode and cathode, said anodehav- 7 ing a cylindrical shape of large surface area,

' chrome-iron member to carry said anode and to serveas anelectri'calconnector therefor.

3. A discharge tube comprising a vitreous entherein, a cathode and acarbonanode disposed within said envelope and forming a discharge path,said anode having a large activecsurface area and being pro- -vided witha large internal cavity to substantially lessen its weight, said cavitybeing completely closed from the discharge path and being void of allnon-gaseous matter, a metal .support member hermetically sealedtosaid-envelope, and

means exclusively supporting said. anode from said member. '4. Arectifier tube for currents of=20 -amperes and more, comprising avitreousenvelope anda gaseous filling therein, athermionic oxidecathode, a cylindrical anode body 'having' a large surface area andbeing provided with ar-closed internal cavity to lessen its weight, andsupporting means for said-anodebody comprising a conductor sealedto thevitreous envelope, said anode body and said supporting means-beingexclusively supported by :the seal between said conductor and saidenvelope. r

5. A discharge tube comprising a vitreous-envelope an anode and acathode disposed therein to iormra discharge space, said .anode having:a large surface area and being provided with an internal cavity tosubstantially lessen-its weight, said cavity-being closed from' thespace within the envelope and being void of non-gaseous matter, andmeans supporting said anode -in'noncontacting spacial relationshipwith'said -envel ope, said means being sealed to-said vitreous envelopeand being *exclusively supported by -the seal.

' 'ope and forming a discharge space, "said "anode havinga large surfacearea and beingprovided with a large internal cavity to substantiallyiessen its weight, said cavity being completely closed fromthe.discharge'space andbeing void of non-gaseous matter, a'metal memberher-,-

-metically sealed tousaidyitreous envelope, land means supporting said fanode from said ..metal member, said anode, supporting emeansfland metalmember being exclusively supported .-by, the seal between saidmetale-member andsaid: :en-

velope. 7 J JQHANNESGIJSBERTUS JOHANNES BRUIJNES. V JOHANNES HENDRIKUS YJQSEPHUSMAARTENS,

